Mulberry Harbours

To provide the essential logistical support of materials, fuel and munitions for the Allied Invasion of Europe in June 1944, artificial harbours would have to be created, since the dock facilities in France were so heavily defended. Prefabricated in concrete sections in England, shipped over the channel and then put together off the flat, open Normandy beaches. The units when reassembled would form long breakwaters with roadways on top of them, on which the vital cargoes could be rapidly offloaded from large supply vessels onto lorries and driven to the front. This was a stupendous engineering exercise, which involved the manufacture (in secret) of 400 concrete components in fourteen different locations from Middlesborough to Plymouth.

Three Phoenix concrete caissons, part of the Mulberry harbour, under construction in Surrey Docks 1944 © IWM H 37607

Among the many construction sites selected for this programme, several were in shallow basins excavated on the banks of the Thames estuary in addition to the four principal dockland sites. Of the latter, one was at Tilbury and another was in the East India Docks at Blackwall, where six units were constructed. The other two locations were in the Surrey Docks, which had a contract for twelve more. Of these, eight were built in the South Dock (to the south of Greenland Dock), while a further four were constructed in the long Russia Dock, to the north of the Greenland.

Given the terrible destruction delivered by the Luftwaffe on the Surrey Docks during the Blitz, this was a chance for the Surreys to fight back. Ironically, the bottom of the South Dock, once drained, had to be raised by 6ft (almost 2m) to form a suitable base to build on: to do this, rubble from London’s bomb-damaged buildings was used. The South Dock components were the Phoenix caissons used to form the Mulberry breakwaters.

Towing a newly completed Phoenix caisson out of the dock and into the Thames in March 1944, en route to Normandy ©Museum of London PLA Collection 33933

The contract to build them was awarded to John Mowlem in late 1943 and all were completed on time. The link to the Greenland was reopened and the South Dock refilled. The Phoenix sections were floated out to the Thames through the Greenland entrance, with just 9inches (23 cms) to spare, on their long journey to join the D-Day landings in Normandy on 6th June.

Text adapted from Andie Byrnes Mulberry Harbours at Rotherhithe’s South Dock.